#main{
    margin: 0 auto;position: relative;
}
#canvas{
    display: block;      
}
#controller{
    position: absolute;
    left: 0;
    display: flex;
    justify-content:space-between;
    flex-direction: row;
}
.op_btn{
    margin: 8px 0 0 8px;
    border: 1px solid #aaa;
    width: 60px;
    height: 32px;
    line-height: 32px;
    font-size: 18px;
    text-align: center;
    border-radius: 5px 5px;
    cursor:pointer;
    background-color: white;
    font-weight: bolder;
}
.op_btn:hover{
    background-color: #def;
}
.color_btn{
    margin: 8px 8px 0 0;
    border: 3px solid #FFF;
    width: 32px;
    height: 32px;
    border-radius: 5px 5px;
    cursor:pointer;
}
.color_btn:hover{
    border:3px solid #69f;
}
.color_btn_selecter{
    border:3px solid #45f;
}
#black_btn{
    background-color: black;
}
#red_btn{
    background-color: red;
}
#yellow_btn{
    background-color: yellow;
}
#green_btn{
    background-color: green;
}
#blue_btn{
    background-color: blue;
}
#purple_btn{
    background-color: purple;
}
